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C $Header: /u/gcmpack/models/MITgcmUV/eesupp/src/read_field.F,v 1.1 1998/04/27 18:54:36 cnh Exp $ |
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#include "CPP_EEOPTIONS.h" |
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SUBROUTINE READ_FIELD_XYZR8( |
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O fld, |
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I filNam, filFmt, myThid ) |
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C /==========================================================\ |
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C | SUBROUTINE READ_FIELD_XYZR8 | |
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C | o Reads a file into three-dimensional model array | |
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C |==========================================================| |
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C | Routine that controls the reading of external datasets | |
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C | into the model. In a multi-threaded and/or MPI world | |
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C | this can be a non-trivial exercise. Here we use the | |
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C | following approach: | |
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C | Thread 1. reads data for the complete domain i.e. all | |
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C | processes and all threads into a buffer. Each individual | |
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C | thread then reads its portion of data into the actual | |
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C | model array. This is clean because there is just one | |
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C | input file with a single format irrespective of the | |
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C | of processes or threads in use. However, it has several | |
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C | potential difficulties. | |
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C | 1. Very large problems may have individual fields of | |
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C | several GB. For example 1/20th degree global and | |
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C | fifty levels is 10GB per field at 8 byte precision. | |
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C | 2. MPI 1.nn is vague about I/O support - not all | |
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C | processes have to support I/O. | |
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C | MPI 2. includes a standard API for distributed data, | |
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C | parallel I/O. If applications funnel all their field | |
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C | I/O through this routine then adopting this or some | |
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C | alternative should be fairly straight-forward. | |
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C | In the light of problem 1. the following strategy | |
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C | is adopted. Files are read one layer at a time. After | |
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C | each layer has been read there is a barrier and then | |
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C | the threads all copy data from the buffer to the arrays.| |
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C | This creates a lower-performance I/O code but reduces | |
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C | the degree to which a single large array is required for| |
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C | the master thread. To be consistent with this binary | |
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C | input files must be written by code of the form | |
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C | WRITE(N) ((array(I,J,K),I=1,Nx),J=1,Ny) | |
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C | rather than of the form | |
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C | WRITE(N) array | |
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C | The approach taken here also avoids one other ugly | |
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C | behaviour. On several systems even Fortran internal | |
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C | reads and writes are not thread-safe. This means that | |
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C | the portion of the code that builds file names has to | |
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C | be a critical section. However, if only the master | |
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C | thread is interested in the value of the file name then | |
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C | only the master need set its value. | |
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C | Finally the IO performed here is for the whole XY | |
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C | domain - even under MPI. The input files can stay the | |
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C | same no matter what processor count is being used. | |
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C | This is not a scalable approach to IO and MPI 2 has much| |
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C | better support for this. Output is handled differently. | |
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C | By default output files are written split and have to be| |
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C | merged in a post-processing stage - YUK! | |
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C \==========================================================/ |
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C == GLobal variables == |
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#include "SIZE.h" |
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#include "EEPARAMS.h" |
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#include "EESUPPORT.h" |
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#include "EEIO.h" |
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C == Routine arguments == |
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C fld - Array into which data will be written. |
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C filNam - Name of file to read. |
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C filFmt - Format to use to read the file. |
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C myNz - No. vertical layers for array fld. |
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C myThid - Thread number for this instance of the routine. |
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REAL fld(1-OLx:sNx+OLx,1-OLy:sNy+OLy,1:Nr,nSx, nSy ) |
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CHARACTER*(*) filNam |
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CHARACTER*(*) filFmt |
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INTEGER myThid |
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C == Local variables == |
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C msgBuf - Variable for writing error messages |
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C I,J,K, bi,bj - Loop counters |
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C dUnit - Unit number for file I/O |
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C ioStatus - I/O error code |
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CHARACTER*(MAX_LEN_MBUF) msgBuf |
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INTEGER I |
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INTEGER J |
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INTEGER K |
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INTEGER bi |
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INTEGER bj |
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INTEGER iG, jG |
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INTEGER dUnit |
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INTEGER ioStatus |
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C |
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dUnit = 42 |
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C-- Open the file |
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C Note: The error trapping here is inelegant. There is no |
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C easy way to tell other threads and/or MPI processes that |
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C there was an error. Here we simply STOP if there is an error. |
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C Under a multi-threaded mode this will halt all the threads. |
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C Under MPI the other processes may die or they may just hang! |
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_BEGIN_MASTER(myThid) |
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OPEN(dUnit,FILE=filNam,FORM='unformatted',STATUS='old', |
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& IOSTAT=ioStatus) |
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IF ( ioStatus .GT. 0 ) THEN |
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WRITE(msgBuf,'(A)') |
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& 'S/R READ_FIELD_XYZR8' |
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CALL PRINT_ERROR( msgBuf , myThid) |
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WRITE(msgBuf,'(A)') |
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& 'Open for read failed for' |
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CALL PRINT_ERROR( msgBuf , myThid) |
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WRITE(msgBuf,'(A,A50)') |
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& 'file ',filNam |
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CALL PRINT_ERROR( msgBuf , myThid) |
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STOP 'ABNORMAL END: S/R READ_FIELD_XYZR8' |
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ENDIF |
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_END_MASTER(myThid) |
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DO K = 1, Nr |
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C-- Read data from file one XY layer at a time |
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_BEGIN_MASTER(myThid) |
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C READ ... |
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DO J=1,Ny |
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DO I=1,Nx |
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IF ( filNam(1:1) .EQ. 'u' ) THEN |
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IO_tmpXY_R8(I,J) = 0.0 _d 0 |
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IF ( J .GT. 15 .AND. J .LT. 24 ) |
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& IO_tmpXY_R8(I,J) = 0.1 _d 0 |
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ELSEIF ( filNam(1:1) .EQ. 'v' ) THEN |
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IO_tmpXY_R8(I,J) = 0.0 _d 0 |
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ELSE |
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IO_tmpXY_R8(I,J) = 0.0 _d 0 |
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ENDIF |
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ENDDO |
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ENDDO |
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_END_MASTER(myThid) |
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_BARRIER |
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C-- Copy data into per thread data structures |
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DO bj=myByLo(myThid),myByHi(myThid) |
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DO bi=myBxLo(myThid),myBxHi(myThid) |
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DO j=1,sNy |
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DO i=1,sNx |
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iG = myXGlobalLo+(bi-1)*sNx+I-1 |
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jG = myYGlobalLo+(bj-1)*sNy+J-1 |
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fld(i,j,k,bi,bj) = IO_tmpXY_R8(iG,jG) |
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ENDDO |
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ENDDO |
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ENDDO |
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ENDDO |
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_BARRIER |
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ENDDO |
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C |
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_EXCH_XYZ_R8(fld, myThid ) |
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C |
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RETURN |
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END |
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